Was there really a great flood?

Hundreds of myths from around the world suggest there was a great flood -- possibly local or­ possibly global, depending on the story. Christians generally believe that this is Noah's flood, a global event brought on by God to cleanse the world of wickedness.­

The scientific community doesn't wholly doubt the possibility of a great flood, but it has yet to answer the questions of where and when it might have happened.

There are two scientific theories in existence, one suggesting flooding around the area that is now the Black Sea and the other attributing devastating floods to a comet that struck the Earth. Let's first look at the more popular hypothesis: the flooding of the Black Sea, also known as Noah's Flood Hypothesis.

In the late 1990s, Columbia University geologists William Ryan and Walter Pitman proposed that a great flood in the Middle East resulted from rising water levels at the end of the last Ice Age about 7,000 years ago. At that time, the Black Sea was a freshwater lake and the lands around it were farmlands. When the European glaciers melted, the Mediterranean Sea overflowed with a force 200 times greater than that of Niagara Falls, converting the Black Sea from fresh to saltwater and flooding the area [source: National Geographic].

National Geographic Society explorer Robert Ballard, inspired by Ryan and Pitman's hypothesis, has discovered supporting physical evidence, including an underwater river valley and ancient shoreline as well as Stone Age structures and tools beneath the Black Sea. His team has also unearthed fossils of now-extinct freshwater species dating back some 7,460 to 15,500 years.

While this theory is still being reviewed, Bruce Masse, an environmental archaeologist at Los Alamos National Laboratory, put forth his own theory about the great flood. He hypothesizes that more comets and meteors than we know have hit Earth throughout its history. He believes the seeds of great flood stories may have sprouted when a comet hit our planet about 5,000 years ago.

Masse's presumption is that a 3-mile (4.8-kilometer) wide comet crashed into the ocean off the coast of what is now Madagascar. The result? Worldwide chaos, including violent 600-foot (182.8-meter) high tsunamis and massive hurricanes spawned when superheated water vapor and aerosol particulates shot into jet streams. All of this terror was accompanied by a week of darkness caused by material expelled into the atmosphere.

Masse's theory derives from clues in cultural flood myths, including ancient petroglyphs, drawings and historical records, but it's the physical evidence he's after to make the case. Since Masse presented his idea in 2004, he's found support in the geological community.

A 600-foot high tsunami would surely leave behind a geological calling card -- and that it did. When waves are generated by such a significant impact, they create wedge-shaped configurations in the sand, known as chevrons, and when the Holocene Impact Working Group went looking for them with satellite imagery, they were able to locate such formations in Africa and Asia. Carbon dating fossils found in the chevrons will help determine if they fit within the proposed 5,000-year timeline.

While we get closer to figuring out if a great, global flood did happen, we also face future massive flooding. Catastrophic floods threaten one billion people today and this number will rise to more than two billion by 2050 [source: United Nations]. The combination of climate change, deforestation, rising sea levels and population growth threatens us with mounting risks for flooding.